The invention concerns new compositions and a new process for improving the efficiency of fossil fuel combustion sources, especially lean-NOx combustors, by reducing the fouling of heat transfer surfaces by unburned carbon while limiting the amount of secondary additive ash. Utilizing a fuel containing a fuel-soluble catalyst comprised of platinum and at least one additional metal also reduces production of pollutants of the type generated by incomplete combustion, e.g., particulates, unburned hydrocarbons and carbon monoxide.
Efforts to improve power generation efficiency have often lead to the use of heat recovery steam generators to obtain additional flue gas heat recovery. This has the advantage of improving cycle efficiency, but unburned carbon can form deposits and reduce heat transfer in these devices. Moreover, the use of combustion catalysts can lead to the production of ash, which can itself reduce heat transfer efficiency unless regular maintenance routines are followed—often resulting in shutting down the process for cleaning.
In some efforts to reduce pollution from diesel engines, natural gas is being employed as an alternative fuel. Unfortunately, difficulties have arisen in obtaining good combustion by compression alone and the natural gas does not readily ignite as it is compressed. In some cases, an ignition source is provided to ignite the natural gas. The ignition source may be provided by a spark plug similar to those used in spark ignition engines. Alternatively, dual-fuel diesel engines can facilitate ignition by injecting a small amount of diesel or other pilot fuel into a mixture of air and gaseous fuel prior to or during compression. In some engines of this type, the generation of soot can be troublesome.
The use of downstream particulate removal systems has gained wide acceptance, but these devices add costs in terms of initial investment and periodic maintenance. It would be desirable to enable combustion under conditions which favored less carbon generation without the need for levels of combustion catalysts that are too expensive or result in ash that would burden particulate removal systems or cause fouling that requires cleaning to maintain efficiency. Moreover, it would be desirable to provide effective and efficient combustion and reduced stack gas opacity without excessive generation of high levels of fine metallic particulates which might escape to the atmosphere.
Some fuel borne catalysts have been identified as health risks and cannot be employed at any level. It would be desirable to utilize nontoxic metal combustion catalysts at low and ultra low levels to achieve improved heat recovery and lower emissions of regulated pollutants.
There is a need for a new low-emissions combustion process to reduce emissions of one or more regulated pollutants which can also be used to reduce carbon or particulates from the combustion gases that may cause smoky emissions or fouling of heat transfer surfaces or downstream heat recovery devices.